This invention relates generally to an N-way power divider/combiner and more particularly to a power divider/combiner employing non-floating, grounded loads to provide adjacent output/input port isolation for coupling to a plurality of power amplifiers or other active or passive devices.
The best known and most commonly used N-way power divider/combiner was devised by E. J. Wilkinson and is fully described in an article which appeared in the IRE Transactions on Microwave Theory and Techniques, Volume MTT-8, pages 116-118 (Jan., 1960) entitled "An N-Way Hybrid Power Divider". While the Wilkinson device offers matched conditions at all ports, a lower insertion loss, and high isolation between output/input ports, it suffers from the disadvantage that the resistive star required is difficult to realize in practice, particularly for a large number of output/input ports. The resistors used in the resistive star limit the power capability of the divider/combiner due to the difficulty of heat sinking of the resistors.
Ullrich H. Gysel of the Stanford Research Center described a modification of the Wilkinson device in his paper entitled "A New N-Way Power Divider/Combiner Suitable for High Power Applications" which appeared in the Proceedings of the 1975 M.T.T. Symposium, Palo Alto, California. The Gysel modified device offered external isolation loads (high-power load resistors) and monitoring capability for imbalances at the output/input ports. However, Gysel offered no means for practical realization of his apparatus other than stating that its construction would be easy in either stripline, slabline or microstrip.
An attempt to implement the Gysel device resulted in a sandwich type structure employing stripline to provide the required quarter wavelength transmission lines. The design was realized on a 1/32" Teflon board in microstrip form. Two separate boards were used and through connections, necessitated by the topology of the design, were made with 1 mm (millimeter) bolts. This apparatus has marked advantages over its cousin the Wilkinson device in that the isolating means are coupled to ground whereas in the Wilkinson device, the isolating loads are floating with respect to ground. By coupling the loads to ground, fabrication problems and the problem of power limitations as described above is avoided. However, it has been found that this type of a structure is not suitable for an apparatus requiring many ports, for example, 24, due to the complexity of the required transmission line pattern and the resultant increase in insertion loss.